The present invention relates to apparatus for applying strapping around an object. More particularly, the invention relates to apparatus for tensioning plastic strapping in a loop around an object and forming a heat-sealed joint in the strap loop for securing it about the object.
The present invention is an improvement of the strapping apparatus disclosed in U.S. Pat. No. 3,944,460, issued to G. A. Karr on Mar. 16, 1976, entitled "COMBINATION STRAPPING TOOL FOR PLASTIC STRAP", and assigned to the assignee of the present invention. That strapping tool has a heat-sealing mechanism including a cam shaft adapted for camming engagement with a movable pressure block and with a rocker arm which is in turn releasably coupled to a movable heater. As the cam shaft is rotated, the rocker arm moves the heater between the overlapping strap portions and the pressure block is moved to press together the heating element and the strap portions for melting thereof. Further rotation of the cam shaft disengages it from the pressure block and decouples the rocker arm from the heater to permit retraction of the pressure block and the heater by separate bias means. Further rotation of the cam shaft again effects cammed movement of the pressure block to bond together the melted strap portions and to sever the supply portion of the strap.
In that prior strapping tool, the pressure block cooperates with a strap guide surface on an anvil-like base member for pressing therebetween the overlapping strap portions, both the strap guide surface and the pressure block having substantially smooth planar pressure surfaces thereon. Because of manufacturing imperfections in producing such surfaces economically, it is not possible with the prior art strapping tool to achieve a truly even distribution of pressure throughout the seal area. Furthermore, it has been found that the bond between the overlapping melted strap portions formed by the prior strapping tool is not sufficiently strong for certain high load applications.